Automotive seating systems are typically designed as part of a host vehicle occupant's protection or safety system. Accordingly, various requirements are imposed on such seating systems. They must have high strength and structural integrity so that the seat remains anchored to the vehicle in the event of a crash, i.e., the seat tracks should not separate from the vehicle, from each other or from the seat. Furthermore, the seat back should either remain in its pre-crash set position, or under certain conditions collapse in a predictable, energy absorbing manner. Test results embodied in U.S. Federal Motor Vehicle Safety Standards 208 and 210 require that the seat belts and their anchorages withstand loads of 1500 to 3000 pounds without failure. If any anchorage is mounted to the seat structure, the structure must withstand such loads as well. The outboard (adjacent the door) upper and lower seat belts and anchorages should withstand the load of 1500 pounds and the inboard (adjacent the center line) lower part should withstand 3000 pounds. In addition, increased emphasis on fuel economy necessitates vehicle weight reduction. This, of course, makes it highly desirable to reduce the weight of the seating system, but mere weight reduction can adversely impact the strength of the seating system.
Cost containment is still another requirement imposed upon automotive vehicle seating systems and prior art attempts to meet all three requirements, high strength--lightweight--low cost, have not been satisfactory. Some attempts have been made to substitute aluminum for steel in the design of seat frame assemblies. These designs typically required steel reinforcements to provide the necessary structural strength and such reinforcements add weight, package size and cost to the systems.
Another desirable advantage of automotive seating systems is the integration of the seat restraints or safety belt means so that the track assemblies, seat and seat belts are a self-contained unit. If the seat belts were integrated with seat and track assemblies, adjustment of the seat by the occupant would not require readjustment of the seat belts. It would also facilitate the installation of the seat belts in convertible vehicles where no pillars are readily available. Usually the seat belts are anchored to the vehicle body pillar and floor to reduce the loads imposed on the seat track assemblies during a crash. Attempts to integrate all of the seat belts with the seat and track assemblies aggravate the strength and weight considerations noted above.
The use of seat back recliner mechanisms further aggravate the shortcomings of prior art designs in that they tend to have an operating range of motion which are limited to fifty degrees or less. Furthermore, they are configured to provide the lowest mechanical advantage when the seat back is in a full down or reclined position wherein an extremely large motor and drive train is required to lift an occupant and seat back to the upright position. A dump feature, necessary to permit entry into the back seat of a two door vehicle, has proven difficult to provide in seating systems which include seat back reclining mechanisms. When such dump features are provided to permit momentary disconnection between the seat back adjuster and the seat back, "chucking" i.e., a slight movement of the seat frame and seat back and looseness in construction evident in an unoccupied seat, presents a further problem.
Finally, in so-called fully structural seats in which all three seat belt anchorage points are born by the seat frame, designs with enhanced strength are required. However, limited passenger compartment space has made the packaging of the foregoing features difficult. A related problem results from the necessity of having a seat frame design which is extremely rigid, particularly when subjected to frontal impact forces, while collapsing in a controlled, predictable and energy absorbing manner upon severe rear impact conditions.